ValueError: invalid literal for int() with base 10, Missing configuration ?

[algorys]

When launching alignak framework with backend module installed, we have the following error raised:

[2018-04-24 07:36:19 PDT] ERROR: [alignak.modulesmanager] The module backend_scheduler raised an exception on loading, I remove it!
[2018-04-24 07:36:19 PDT] ERROR: [alignak.modulesmanager] Exception: invalid literal for int() with base 10: ''
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/alignak/modulesmanager.py", line 253, in get_instances
    instance = python_module.get_instance(alignak_module)
  File "/usr/local/lib/python2.7/dist-packages/alignak_module_backend/scheduler/module.py", line 54, in get_instance
    return AlignakBackendScheduler(mod_conf)
  File "/usr/local/lib/python2.7/dist-packages/alignak_module_backend/scheduler/module.py", line 86, in __init__
    self.backend_count = int(getattr(mod_conf, 'backend_count', '50'))
ValueError: invalid literal for int() with base 10: ''

It seems that when we add the following line, in the scheduler configuration file:

 backend_count             50

... this error disappears.